1. Field of the Invention
This invention relates to an optical apparatus such as a camera or the like and, more particularly, to an optical apparatus having an image forming optical system arranged to be capable of carrying out a magnification varying action and a focus adjusting action and a viewfinder arranged to display images at a magnifying rate which varies according to the magnification varying state of the image forming optical system.
2. Description of Related Art
In the field of the lens-shutter type cameras which are arranged to have viewfinder optical systems separately from photographing optical systems, it has recently become popular to arrange them to be equipped with zoom lens barrels. The cameras arranged in this manner are called zoom cameras in general. Each of such zoom cameras is arranged to cause the viewfinder optical system to vary its magnification in association with the magnification varying action of the photographing optical system.
Generally, the lens-shutter type cameras are desired, as a designing target, to be small in size, light in weight and low in manufacturing cost. To attain the designing target, for example, the following contrivances have been proposed.
(a) Japanese Laid-Open Patent Application No. HEI 5-173223.
A viewfinder optical system is arranged to be moved by a lever which moves following the magnification varying action of a lens barrel of a photographing optical system.
(b) Japanese Laid-Open Patent Application No. HEI 2-24613.
One and the same motor is arranged to be used for both focusing and zooming actions.
(c) Japanese Laid-Open Patent Application No. SHO 64-84233.
One and the same motor is arranged to be used for focusing and zooming actions through a helical bar.
(d) Japanese Laid-Open Patent Application No. SHO 61-259237.
A single cam groove in a zigzag shape is formed in a cam plate by connecting one end of each of a plurality of focusing cam grooves and a plurality of zooming cam grooves extending in respective different directions to one end of another. One and the same cam plate formed in this manner is arranged to be used for focusing and zooming actions which are alternately performed by a photographing optical system.
(e) Meanwhile, a camera has been commercialized, in which a viewfinder optical system is moved through a cam in association with a photographing optical system which alternately performs focusing and zooming actions according to a cam plate similar to the above-stated cam plate disclosed in Japanese Laid-Open Patent Application No. SHO 61-259237. The action of the cam makes the viewfinder optical system stationary when the photographing optical system is performing the focusing action, and causes the viewfinder optical system to perform its magnification varying action in association with the photographing optical system when the photographing optical system performs its magnification varying action.
In the case of the camera mentioned in Paragraph (e) above, a cam follower of the photographing optical system moves alternately in a magnification varying area and a focus adjusting area of the cam, for example, when the position of the photographing optical system is moving from a telephoto end position toward a wide-angle end position. Accordingly, the size of an image obtained in the viewfinder continuously varies in the magnification varying area of the cam but does not vary in the focus adjusting area of the cam. Therefore, the image magnifying rate in the viewfinder comes to intermittently change. The intermittent change has presented a problem because it gives an unnatural, unpleasant impression to the operator of the camera who looks into the viewfinder.